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<h2><a name="SECTION0015420000000000000000">
13.4.2 Example</a>
</h2>

<p>
To summarize the interface (<code>key</code> is a string, <code>data</code> is an
arbitrary object):

<p>
<div class="verbatim"><pre>
import shelve

d = shelve.open(filename) # open -- file may get suffix added by low-level
                          # library

d[key] = data   # store data at key (overwrites old data if
                # using an existing key)
data = d[key]   # retrieve a COPY of data at key (raise KeyError if no
                # such key)
del d[key]      # delete data stored at key (raises KeyError
                # if no such key)
flag = d.has_key(key)   # true if the key exists
klist = d.keys() # a list of all existing keys (slow!)

# as d was opened WITHOUT writeback=True, beware:
d['xx'] = range(4)  # this works as expected, but...
d['xx'].append(5)   # *this doesn't!* -- d['xx'] is STILL range(4)!!!

# having opened d without writeback=True, you need to code carefully:
temp = d['xx']      # extracts the copy
temp.append(5)      # mutates the copy
d['xx'] = temp      # stores the copy right back, to persist it

# or, d=shelve.open(filename,writeback=True) would let you just code
# d['xx'].append(5) and have it work as expected, BUT it would also
# consume more memory and make the d.close() operation slower.

d.close()       # close it
</pre></div>

<p>
<div class="seealso">
  <p class="heading">See Also:</p>

  <dl compact="compact" class="seemodule">
    <dt>Module <b><tt class="module"><a href="module-anydbm.html">anydbm</a></tt>:</b>
    <dd>Generic interface to <code>dbm</code>-style databases.
  </dl>
  <dl compact="compact" class="seemodule">
    <dt>Module <b><tt class="module"><a href="module-bsddb.html">bsddb</a></tt>:</b>
    <dd>BSD <code>db</code> database interface.
  </dl>
  <dl compact="compact" class="seemodule">
    <dt>Module <b><tt class="module"><a href="module-dbhash.html">dbhash</a></tt>:</b>
    <dd>Thin layer around the <tt class="module">bsddb</tt> which provides an
  <tt class="function">open</tt> function like the other database modules.
  </dl>
  <dl compact="compact" class="seemodule">
    <dt>Module <b><tt class="module"><a href="module-dbm.html">dbm</a></tt>:</b>
    <dd>Standard <span class="Unix">Unix</span> database interface.
  </dl>
  <dl compact="compact" class="seemodule">
    <dt>Module <b><tt class="module"><a href="module-dumbdbm.html">dumbdbm</a></tt>:</b>
    <dd>Portable implementation of the <code>dbm</code> interface.
  </dl>
  <dl compact="compact" class="seemodule">
    <dt>Module <b><tt class="module"><a href="module-gdbm.html">gdbm</a></tt>:</b>
    <dd>GNU database interface, based on the <code>dbm</code> interface.
  </dl>
  <dl compact="compact" class="seemodule">
    <dt>Module <b><tt class="module"><a href="module-pickle.html">pickle</a></tt>:</b>
    <dd>Object serialization used by <tt class="module">shelve</tt>.
  </dl>
  <dl compact="compact" class="seemodule">
    <dt>Module <b><tt class="module"><a href="module-cPickle.html">cPickle</a></tt>:</b>
    <dd>High-performance version of <tt class="module"><a href="module-pickle.html">pickle</a></tt>.
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<span class="release-info">Release 2.5.1, documentation updated on 18th April, 2007.</span>
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